Method of recording sound



Dea l0, 1940- M. J. c. VAN DER MEULEN 224mm METHOD OF RECORDING SOUND Filed Feb. 9, 1939 i. :E if

Patented Dec. `10, 1940 N I #UNITED STATES 2,224,170l l I METHOD F RECORDING SOUND 'v Marius Johannes Cuinirus van der Meulen, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application February 9, 1929, Serial No. 255,518 Y In Germany February 17,1938

Claims.

`This invention relates to a method of electromechanically recording sound vibrations in which a sound track of variable depth is p-roduced on a carrier by a cutting tool.

Although not limited thereto, my invention` is particularly radapted for'use in recording of the type described in the U. S. Patent #1,919,116 to James A. Miller, and I shall describe the same in connection therewith.

In such recording, a `cutting tool having a V-shaped cutting edge with a large apical angle is vibrated in accordance with the sound being recorded and perpendicularly to the Surface of a carrier'provided with an opaque covering layer,

to remove portions of the covering layer and thereby produce an optically-reproducible sound track having `depth variations and corresponding y Width variations. I havefound that when reproducing a sound track recorded in this manner therey is frequently deformation in the reproduced sound although the originally-recorded sound wasfree from deformation. I have :found that such deformation is `inherent to recording systems which produce lvariable dep-th sound tracks, and is due tothe :fact that the cutting tool `when moving into the cutting layer of the carrier, i.` e'. during'the movement of penetration, meets with a greaterresistance than when it is moving out -of the carrier, i. e. during the move- 30. ment of recession. Consequently the movement oi penetra-tion of the cutting tool is retarded relative to the movement of recession, and all of the sound curves are deformed in one direction. This deformation becomes manifest during the reproductionby the presence of higher overtones.

lThe object of my invention is tovovercome they above'diihculties, and for this purpose I introduce, during the re-recording of the originally-recorded record on a second carrier, distortions which com- 4 A pensate the distortions produced during the recording.' More particularly, I use the distortions.

introduced in the original record to compensate the` distortions in the record. For this purpose, I `scan theoriginally-recorded sound track 4to produce electrical vibrations, re-record said vibrations with a recording system which is identical with; that used ,during the recording and rotate the phase position of these electrical vibrations y by 180 to produce electrical vibrations which are used in the re-recording.

Thus during the re-recording the deformations present in the rst record are scanned and are fed .to the recording device, but due to the 180 phasejdisplacement they are just in opposite 55, phase with the deformations which are intro- (o1. 17o- 10mn duced during Vthe re-recording on the second carrier. Thus the deformations `caused by the recording System are eliminated as completely as possible.

In order that the invention may be clearly understood vand readily carried into effect, I shall describe the same in more detail With reference to the accompanying drawing, in which;

Figure 1 is a diagrammatic view of 'a recording `device formechanically recording an opticallyreproducible sound track having both depth and Width variations,

Fig. 2 is a plan view of a carrier with a sound track therein, ,v .I

Fig.'3 is a diagrammatic View of a re-recording device for carrying out the invention, and

Fig. 4 is a diagrammatic View of a re-recording device according to another embodiment of the invention. u t y 'Ihe recording system illustrated in Fig. 1 comprises a microphone I0 having terminals II and 'I2 connected to terminals I3 and I4 respectively of a pre-amplifier I5. Pre-amplifier I5 has `output terminalsV I6, and` I'I connected to input terminals 4 I8 and. I9 respectively of a recording amplier 20 for the purpose of conducting the electrical sound vibrations. The electrical energy is conductedfrom output terminals 2| and 22 of amplifier 2li to the terminals 23 and24 of a sound recorder `25having an armature carrying acutting tool 26 provided With a V-shaped cutting edge having an apical angle of about 174. A suitablerecorder for this purpose has been described in U. S. Patent #2,108,275 to Vermeulen et al. I

The electrical energy supplied to terminals 23` `and 24 actuates` cutting tool 26 to produce in a lm carrier 21 a `sound track corresponding to the sound vibrations striking microphone I0. Carrier 21, Which may be of the type described in U. S. Patent #2,020,861 to van der Willigen etal., comprises three layers, namely a supporting layer of Celluloid, an intermediate cutting layer of gelatin, and a thin opaque covering layer. During' the recording, the cutting tool 26 is vibrated perpendicularly to the carrier to` remove portions of the opaque layer, and because of the large apical` angle of" its cutting edge, theresulting opticallyreproducible sound track 28 has depthvariations, `and corresponding width Variations Which are a proportional enlargement of the depth variations.

During that part of its motion in which it movesr into the cutting layer, the cuttingtool 26 meets with a greater resistance than when it ZCIl tions of the covering layer of the film. ,During1 the motion of penetration of the cutting tool its movement, which incase of sound recorded free.

from deformation extend sinusoidally according to time, is retarded. As the carrier 2l is moved with a constant velocity, the portions 'of the boundaries of the sound track are straighter'than .i those of the, correct sine curve 46. Duev tothis,V i

however, the position of the cuttinglags with respect to the electrical sound curve in the recordng device, and duringits movements of recession the movement of the cutting tool is `accelerated with the result that the portions 418 are steeper than those of the correct sine curve dij. Thus, the Ycorrect sine curves are deformed into the curves-45, and this deformation becomes manifest during the reproduction as overtones of the recorded frequencies.

In Fig. 3 thesound track 28 obtained in the manner described above in connectionwith Fig. 1 is scanned opticofelectrically. For this purpose an objective 3l projects a line of light 32 upon carrier 2, and the variations in light produced by sound track 28 are converted by a photoelectric Acell 33 into electrical oscillations which are conducted from the terminals 34-and 35 of the photocell to the terminals 36 and 37 of a scanning amplifier d. The phase position of the amplitudes of the electrical variations at the output terminals 3S, andAiJ of amplifier 38 is the samelasV that yof Athe electrical variations at the output terminals I6 and I'I ofthe pre-amplifier I5 of Fig. 1. However, during refrecording the connections between the pre-amplifier 38 and the recording amplifier 20 of Fig. 1. are reversed. More particularly, as shown in Fig. 3, the terminals 39. and 40, which correspond to the terminals i6 and Il respectively of the microphone ampli'- fier I5 of Figure 1, are connected tothe input terminals I9 and I8 respectively'. As a resultthe phase` position of the amplitudes at the terminals I8. andl9 of the amplifier 20' during. re-recording.

is displaced exactlyi80relative to the rst record.

. As shown in Fig. 3, the re-recording is effected with the same recording system and recorder 25 as in Fig. 1, and consequently the same deformation of the recorded frequencies would necessarily be introduced. However, due to the reversal ofk thephase position at the terminals I8 and I9, the deformations arefdisplaced in phase by 180 relative to those present inthe rst-recorded track 28, so that the sound track 4I obtained after recording on a second lm 42 is free from deforming overtones caused by the recording method.

` In carrying this method of re-recording into effect it is absolutely necessary that during rereversed.

same sound recorder 25'are used for both the recording and re-recording.

A l1n the embodiment of the invention illustrated in Fig. 4 the same reference numerals indicate the 'same parts. In vthis case the required dis- Y placementlof the phase position by 180 from that at' the inputr side of the recording amplifier is obtained by the interposition of a filter i3 between the pre-amplier 33 and the-recording amplifier 2i). In fact, it will frequently occur that in the optico-electrical scanning of the sound track 28, the phase position at the output terminals 39 and di? is not identical to that during recording at the, terminals ,I6 and I'I of the microphone amplifier. ;.To produce the .desired v180 change in phase position at the terminals I8 and I9 durf ing re-recording, relative, to theg phase position at theseterminals, during the first recording, it is necessary to utilize a phase rotation Vfilter 13,4 which together with the prefamplifier 38, causes a phase rotation of 180 relative tothe phase.

position during the rst recording at the terminals i8 and it of the recording amplifier 20, at least forthat frequency range, in ,which the deformation stated above becomes most manifest, for example from 2000 tolOOO cycles According to this embodiment of the inventionthe rerecorded sound track`will therefore be freefrom overtones brought aboutvby the recording method at Vleast ina certain selectable frequencyY range. In Aa third embodiment of the inventiom'which is not illustrated in vthe drawing, I move the carrier, during scanning and re-recording of the iirst` record, in a direction opposite to thatin which itwas moved during the recording of this record. In this mannera ,displacementmof the.

phaseposition of 180 is obtained throughout theY frequency rangean'd the second record, whichjisv of jcourse to be `moved atreproduction in aldirece tion opposite to the vmovement at its recordingris freefromvlthe overtones" causedbythe system of recording. More particularly, in Fig. 3 the care rierwould be moved opposite to the direction of arrow 44, andthe connections between V terminals 3 9, and 'til and terminalsl VI8 and I9Vwouldnot be I, have found that in the latter caseit can be ascertained through the nature of` thesound trackwhether the record has been {recorded in the natural order of the soundor has been proposed by scanning and rfc-recording the first record moving in a direction Oppositeto11net. of `thev original recording. VI know-'from experienethatA on recording in the formof depth variations in a gelatin layer the surface of the track when .the

chisel is being lifted .outis notonly-cutl Vbutis planed to a less. or. greater' extent.v- A planed gelatin surface becomes frosted Particularly `in` case of .steep `slopes offth'e cuttings, i. epa'high frequencythis planing "causes a clearly visible frostedsurface. 'i f 1 Y With ya recordV of the Ii'iatu'ral,order of'the sound the slopes 48''offthe"curve'sofV Figi Z-are located on` the side of; the" cuttings lopposite 4to that of thedirectionin whichvfthe lm moves lduring cutting and-this side becomes frosted. A

record proposed by'scanninfgand ref-recording of.

theoriginal record moved fin' a direction oppo- 1-'5 site to that of the recording is characterized in that the frosted slopes of the sound curve are located at the front of the cuttings when seen in the direction of reproduction of therecord. In this case the slopes 41 of the sound track have become frosted.

While I have described my invention with reference to specific examples and applications, I do not Wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in View of the prior art.

What I claim is:

1. A method of electro-mechanically recording sound, comprising the steps of mechanically recording on a carrier an optically-reproducible sound track having depth variations, scanning the sound track toproduce electrical vibrations, displacing the electrical oscillations 180 in phase with respect to the first recording, and feeding the oscillations to recording means identical with those used in the recording to re-record the sound track on a second carrier similar to the iirst carrier.

2. A method of electro-mechanically recording sound, comprising the steps of mechanically recording on a 'carrier an optically-reproducible sound track having depth Variations, scanning the sound track to produce electrical vibrations, displacing the electrical oscillations in a predetermined frequency range 180 in phase withv respect to the first recording, and feeding the oscillations to recording means identical with those used in the recording to re-record the sound track on a second carrier similar` to the rst carrier.

3. A method of electro-mechanically recording sound, comprising the steps of mechanically recording on a carrier an optically-reproducible sound track having depth variations, scanning the sound track While moving the carrier in a direction opposite to that in which it Was moved during the recording to produce electrical oscillations,` and feeding the oscillations to recording means identical With those used i-n the recording to re-record the sound track on a second carrier similar to the first carrier.

4. A method of electro-mechanically recording sound, comprising the steps of mechanically recording on a carrier an optically-reproducible sound track having depth variations, scanning the sound track to produce electrical oscillations `having the same phase position as the electrical oscillations employed in the recording, feeding the latter oscillations to ya recording amplifier in 180 phase displacement, and feeding the oscillations produced by the amplifier to recording means identical with these used in the recording to re-record the sound track on a second carrier similar to the first carrier.

5. A method of electro-mechanically recording sound, comprisingY the steps of mechanically recording on a carrier an optically-reproducible sound track having depth variations, scanning the sound track to produce electrical oscillations, passing theoscillations through a filter to eiect for a certain frequency range a phase displacement of 180, and feeding the displaced oscillations to recording means identical with those used in the recording to re-record the sound track on a second carrier similar to the first carrier.

MARIUS JOHANNES CUINIRUS i VAN DER MEULEN. 

